Because linear actuators can be driven with little loss by employing a spring therein for utilizing a resonance phenomenon, they have been used as compressor motors. Because the compressors employing such linear motors exhibit excellent performance such as high efficiency, it is expected that such compressors will be used for refrigerators, freezers, and air conditioners.
As a linear actuator, a voice coil motor is known. In the voice coil motor, electrical current is made to flow through a coil within a magnetic field formed by permanent magnets so that a force to drive the voice coil motor is applied to the coil. Such a voice coil motor is referred to as a movable coil type in which a movable element including a coil is moved.
Another type of linear actuator is also known, in which the permanent magnets and the coil are switched with each other in contrast to the above-mentioned movable coil type, and which is referred to as a movable magnet type in which a movable element including a permanent magnet is moved.
In the linear actuator of movable coil type, a problem is encountered in that reliability is inferior because the movable element includes a coil, electrical current must be supplied to the movable element, and feeder lines may be cut due to the movement of the movable element.
In addition, in the linear actuator of movable magnet type, a problem is encountered in that it is difficult to improve performance because the weight of the permanent magnet is increased when high magnetic flux density is to be obtained, and the weight of the movable element is increased.